Numerous applications resort to multilayer structures combining at least one layer of elastomer material with one or more layers of rigid materials, in order to confer a damping capacity on the structure. Mention may be made, as such, of damping pads for engines or layers of elastomers applied to sheet metals, for example for motor vehicle hoods or casing covers.
Elastomer materials are generally prepared from viscoelastic solid or pasty masses and only acquire their property of damping after crosslinking or vulcanization. It is for this reason difficult to manufacture multilayer structures comprising a layer of elastomer material spread homogeneously and continuously. Apart from the esthetic aspect, the presence of air bubbles in the elastomer layer is liable to weaken the structure. Conventional techniques, such as injection molding, are not very suitable for the manufacture of parts of complex geometry.
Furthermore, the manufacture of damping multilayer structures normally requires a large number of stages: at least one stage of molding a part made of noncrosslinked elastomer of the desired geometry, a stage of crosslinking or vulcanizing this part and a stage of assembling this part with the other part or parts of the structure are generally necessary. The assembling stage, which is generally carried out by adhesive bonding, is a critical operation since it conditions the subsequent strength of the structure: it requires carrying out a first stage of preparation of the surface of the parts to be assembled, for example by degreasing, sandblasting or chemical attack, a second stage consisting of the application of a bonding primer and, finally, a third stage of application of an appropriate adhesive. Furthermore, the presence of intermediate layers, such as the bonding primer and the adhesive, between the elastomer material and the other constituent materials of the structure are liable to considerably reduce the damping efficiency of the system.
Alternatively, the noncrosslinked pasty mass of elastomer can be applied to the surfaces to be treated and then the combination can be cured under a press but this technique does not make it possible to fill in voids which are difficult to access.
There indeed exist certain elastomer materials, such as the polyurethanes, which exhibit the advantage of being able to be employed in a liquid state, and thus of easily filling the molds in order to manufacture parts of complex geometry but these are systems which are highly reactive and require the use of protective equipment during their use as a result of the toxicity of certain reactants.
Another problem lies in the lack of adhesion and of wettability of conventional elastomer materials, which is the cause of premature failure of the structure at the interface between the elastomer material and the other materials which constitute it.
Furthermore, once conventional elastomers are damaged by tears or microcracks, their use in damping may be detrimentally affected to a considerable extent, which requires dismantling and repairing operations.
Finally, the known multilayer structures do not provide, or at least not permanently, a sufficient damping potential.
There thus exists the need to solve, at least partially, the abovementioned problems.